The present invention relates to methods for curving, or bending in the usual terminology in the art, a tube that is cylindrical or substantially cylindrical, or the like, i.e. of a general shape that even if not purely cylindrical can be considered as having that shape, said substantially cylindrical shape being optionally circularly symmetrical, and optionally rectilinear.
The present invention also relates to apparatus for implementing such methods, having applications that are particularly, but not exclusively, advantageous in making fluid admission and exhaust tube necks for motor vehicle engines.
Methods already exist for curving or bending a cylindrical tube or the like. The simplest method consists in exerting forces on the two segments of tube situated on either side of the location where the bend is to be made, said forces tending to bring said two segments angularly towards each other. That solution presents major drawbacks that are described below.
The tube flattens where it is being bent, thereby changing the size of its cross-section which can constitute a fluid-flow constriction that is unacceptable in certain applications. In addition, cracking occurs at the bend, which weakens the strength of the tube wall and can lead to leaks.
To mitigate those drawbacks, an angularly-deformable guide is placed inside a tube such as a string of cone inserts hinged one after another so that while the tube is being bent, its inside section remains substantially constant.
However, that method still presents a drawback because it can be used only if the segments situated on either side of the bend are relatively long and if the radius of curvature is quite large. It therefore does not enable a sequence of relatively tight bends to be made close to one another.